Concrete dowels are embedded into joints between adjacent slabs of concrete to prevent vertical displacement between the slabs to maintain a smooth pavement surface and increase the strength of the concrete in the region of the joint. While the dowels are provided to prevent excessive vertical displacement between the slabs, they are typically designed to allow a small amount of horizontal separation and lateral displacement between the slabs to relieve internal stress to accommodate drying shrinkage and thermal expansion and contraction of the slabs. This permits a normal amount of slab movement to prevent excessive cracking while still maintaining a smooth top surface of the pavement.
Traditionally, two foot lengths of rebar rods were used as the concrete dowels. But rod dowels tend to cause cracking in the concrete due to concentration of the stress on the relatively small surface area of the rods. Concrete dowels configured as larger bars and load plates were therefore developed to reduce cracking by increasing the surface area of the dowel. In comparison to rebar rods historically used as concrete dowels, larger dowel bars and plates provide a flat and significantly increased dowel surface area to improve the dowel's load transfer capability and reduce the tendency of cracking to form at the dowel location. U.S. Pat. No. 6,354,760 and U.S. patent application Ser. No. 11/109,781 describe examples and the benefits of this approach.
To assist in embedding the dowels within adjacent slabs of concrete while the concrete is being poured, dowel devices including dowel bars (or plates) and sleeves have been developed. U.S. Pat. No. 6,145,262 describes this approach. The sleeved dowel bar has the benefit of permitting the bar to slide within the sleeve to accommodate a small amount of horizontal separation between the slabs to relieve internal stress. To accommodate lateral displacement between the slabs the sleeve is a little bit wider than the bar, which allows the bar to move laterally within the sleeve after the concrete slabs have cured. But simply making the sleeve wider than the bar removes positive registration between the bar and sleeve making it difficult to determine when the bar has been properly centered within the sleeve. As a result, construction workers have to install the bars carefully to ensure the proper spacing on either side of the plate within the sleeve, which can be a lot to ask of construction workers in some setting. To solve this problem, the sleeve described in U.S. Pat. No. 6,145,262 contains fins along the side walls of the sleeve to help align the dowel bar within the sleeve.
However, providing dowel sleeves with elongated fins along the interior side walls is an expensive solution. Including the fins along the internal surfaces of the sleeve complicates the manufacturing process and can require multiple molds to create the sleeve. Although a structure containing the fins may be manufactured separately and inserted into to the sleeve after the sleeve has been molded, this significantly complicates the manufacturing process and increases the cost of the dowel. For example, manual assembly steps may be required to insert and secure the fins within the sleeve.
In addition, even when fins are included, it is still possible with prior sleeved dowel devices to install the bar on a slant deflecting the fins prior to pouring the concrete slabs, which can reduce or eliminate the effectiveness of the fins. A plate installed on an angle within the sleeve with the fins deflected before the concrete is poured reduces or eliminates the lateral play that the dowel was designed to allow. With this system, it can also be difficult for the construction workers in the field to see whether the fins have been deflected when the plate is inserted, leading to some portion of the plates being installed without proper alignment within the sleeves.
As a result, there is a persistent need for a lower cost and more reliable concrete dowel solution and, more particularly, a need for a concrete dowel device to ensure proper registration of the plates within the sleeves without requiring cumbersome manufacturing or assembly procedures.